Thermal limit relay



1,627,816 y G. H. WHITTINGHAM THERMAL LIMIT RELAY Filed April 16, 1925 [N VENTOR M B Y A4 A TTORNE V Patented May 10, 1927.

UNITED STATES PATENT OFFICE.

GEORGE H. WHITTINGHAM, OF BALTIMORE, MARYLAND, ASSIGNOR T0 MQNITOR CONTROLLER COMPANY, OF BALTIMORE, MARYLAND, A CORPORATION OF MARY- LAND.

THERMAL LIMIT RELAY.

Application filed April 16, 1925. Serial No. 23,526.

This invention relates to a thermal limit relay, having various uses, but adapted particularly for use in connection with certain other devices for starting alternating electric motors, and for disconnecting the motor from the supply circuit in case of overloading of the motor, or in case of such derangement of one of the circuits of a multi* phase motor as would cause excessive current to flow in the other circuits ofthe motor, all as described in my Patent No. 1,454,022, dated May 1. 1.923. In the patent referred to. I have shown a relay in which the thermal responsive devices are each composed of a corrugated tube and a plain tube, one fitting within the other, and an expansible liquid filling the spaces between the tubes, the inner tube forming a pocket or housing for the reception of a heating ele ment. In the present invention, each thermally responsive device comprises a housing composed of a flat metal strip wound into the form of a helix, the convolutions of which fit closely together and form a tube, and one end of this tube is closed by a cap or plug so that the tube and plug form a housing for the heating element. The tube is arranged vertically on a support, with the open end of the tube lowermost and secured to the support, and on the plug or cap 1s a laterally extending arm for operating the contact member of the relay. The heating element is insertable into the housing through the lower open end thereof. Normally, the convolutions of the helix meet edge to edge and prevent the flow of air through the housing and the escape of heat, except as the heat is carried off by conduction through the metal and radiation. Upon an excessive flow of current through the heating element, the tube expands and un winds and operates the switch.

In the accompanying drawing,

Fig. 1 is a front elevation of a thermal relay made in accordance with my invention;

Fig. 2 is a section on the line 22 of Fig. 1, the switch arm being shown in side view; Fig. 3 is a central vertical section through one of the thermall responsive devices; and,

Fig. 4 is a detail perspective View of the lower part of the bracket.

Referring to the drawing, a represents a.

suitable base, of insulating material, upon which 1s mounted a switch 6, comprising a contact arm 1, hinged at one end to a metal support 2, and carrying at its oppositeend two contacts 3 and 4, adapted to engage stationary contacts 5 and 6, respectively. The contact 3 is connected by a spring 3 to the arm 1 and is arranged so that when the switch is closing the contact 3 will engage the contact 5 before the contact 4 engages the contact 6, and when the switch is openmg, the contact 4 will leave the contact 6 before the contact 3 leaves the contact 5. The switch arm is normally pressed toward closed position by a spring 7. This switch is substantially the same as the relay switch in the patent above referred to.

The switch is operable by either one of the thermostats indicated at c and 0'. These thermostats are alike. Each comprises a bracket 8 consisting of a fiat strip of metal secured in vertical osition upon the base a and having its on s 8 and 8 turned outwardly from the base. as shown. The lower end 8 of the bracket has a circular opening 8 and also a slot 8", extending from one of its sides to said opening. Into the opening 8 is fitted and secured a vertically arranged metal helix 9 composed of two metals hav- 1mg different co-efiicients of expansion, and the upper end of this helix is closed by a plug 10. having a spindle 11, which has a bearing in an opening 12 in the upper end 8 of the bracket. An arm 13, secured to the cap or plug 10, projects laterally from the plug. In assembling the helix in the bracket, the helix is inserted through the opening in the lower part of the bracket and the arm 13 passes through the slot 8 and the pintle on the plug is inserted in the opening 12. The helix is then turned until the arm is in its proper position, and the lower end of the helix is then secured by soldering, or otherwise, to the lower arm of the bracket. The arm 13 extends to a point between the switch arm and the base a where it may engage an adjusting screw 14 on the switch arm. Thus, as shown in Fig. 1, the switch arm has two adjusting screws 14:, each adapted to be engaged by one of the thermostat arms 13. Normally, the arms 13 are out of engagement with the ad Hsting screws 14, but if the helix of either one of the thermostats becomes heated, it will untwist to a certain extent and its arm 13 will engage the adjusting screw 14 and move the switch to open position.

a housing into which a heating element e may be inserted, through the bottom of the tube. This heating element, as shown in the drawing, consists of a metal coil of suitable form and it i connected in an electric circuit (not shown). When a normal current is flowing in the coil very little heat is given oti' and the thermostat will not operate to open the switch; but when there is an excessive flow of current in the coil, the thermostat metal "will expand and open the switch. By having the convolutions of the helin tit closely together so as to form a tube and by closing the upper end of this tube, a pocket is formed from which the heat will not escape except by conduction and radiation as there will be practically no circulation of air through the helix. By reason of this construction, the thermostat may be made more sensitive to fluctuations in temperature of the heating element than if the convolutions of the helix were spaced apart to permit of a circulation of air through the helix.

What claim is:

1. In a circuit controlling device, a thermostat comprising suitable support, a housing on said support composed of a flat oi-metallic strip wound into the form of a helix the conrolutions of which fit closely together and form a tube, and a part closin one end of said tube, the other end of said tube being open. said housing having its open end secured to the support and having its closed end uppermost, and an electric heating element insertable through said open end into the housing.

2. In a circuit-controlling device, a bracket having supporting arms arranged one above the other, a housing between said arms composed of a fiat bi-metallic strip wound into the form of a helix the convolutions of which fit closely together and form a tube, and a part closing one end of said tube, the other end of said tube being open, said part having a bearing in the upper one of said arms, and the open end of the tube being secured to the lower arm of the bracket, and an electric heating element insertable into the tube through its open end.

3. In a circuit-controlling device. a bracket having supporting arms arranged one above the other, said arms having coucentric openings and the lower arm having a slot meeting the opening therein, a housing between said arms composed ota flat bi-metallic strip wound into the form of a helix the couvolutions of which fit closely together and form a tube, and a closure for one end of said tube, said closure having a bearing in the opening in the upper arm.

and having a laterally projecting mcn'iber adapted to pass through the slot in the lower arm, and the opposite end of said tube being open and secured to the lower arm of the bracket and registering with the opening therein, and an electric heating element insertable into said tube through the open end of the latter.

4. In a circuit-controlling device, a switch arm normally pressed towards its closed position, two thermostats, one arranged at each side of the arm, each ther mostat composed of a flat bi-metallic strip wound into the form of a helix the convolutions of which fit closely together and form a tube, and a part closing one end of said tube, the other end of the tube being open, said tubes being arranged with their closed ends uppermost, and having members projecting from said ends beneath the switch arm, and electric heating elements within said tubes.

In testimony whereof I hereunto allix my signature.

GEORGE H. WHITTINGHAM. 

